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Advisory VNAV doesn't quite reflect the real plane.


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So I’ve noticed an issue with the advisory VNAV indicator (the snow flake). In reality the snow flake acts similar to a raw data glide slope indicator. It shows the pilot their position relative to the actual position of the glideslope (or descent path in the case of the advisory VNAV). The problem I’ve noticed is that the snowflake seems to be programmed more like a flight director. A flight director will show the pilot where they need to position to nose in order to maintain or ATTAIN the path they want. The advisory VNAV isn't designed to give the pilot any information on how to get back on the slope other than telling them whether they're above or below it.

 

As an example, if I start my descent too late then I will be well above the path. It doesn’t matter what rate I begin to descend at. The snowflake will show me that I’m above the path until I intercept the actual path (this is exactly how a raw data glideslope indicator works). Unfortunately this isn’t how it’s programmed in the Aerosoft CRJ. It’s programmed to act more like a flight director. So, in my example above, if I’m well above the slope, then as soon as I start a descent at a rate that will get me back on the slope (even though I may be nowhere near the slope yet), the snowflake will be centred. This is not how it operates in real life. The snowflake should only ever be centred when you are physically on the proper descent path. Again, just like the raw data glideslope indicator. I suppose it’s possible that it was programmed this way intentionally as it is a bit easier. If that’s the case then I apologize but I just wanted to clarify that as it currently designed, it does not reflect the real plane.

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Yeah, it is wrong. It should essentially work exactly the same as the Glide slope indication does. But to the most restrictive fix on the arrival, not necessarily the next one. It’s kind of hard to explain exactly what it does, but essentially the advisory VNAV will draw out angles based off of whatever angle is put into the VNAV page 3.0 3.5 etc. and it looks at which of those lines is the most restrictive aka. Requires you to be the lowest and that’s what it shows you. Often it will not be giving you guidance to the next fix but rather a more restrictive one further down the line. Also should be noted that it will only draw these lines for altitude restrictions for waypoints that you have to cross either at an altitude or at or below an altitude. It will not draw anything for a fix that is crossed at or above an altitude. If Hans wants a video I’ll be glad to explain exactly what it does just let me know.

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vor 23 Stunden , Chaxterium sagte:

it’s possible that it was programmed this way intentionally as it is a bit easier

 

...I disagree - after reading your very informative and detailed post I believe the RL snowflake behavior as you describe it is actually easier to understand and follow for the pilot, as it is very intuitive.

 

I hope Hans will have a chance to correct the snowflake behavior in the not too distant future... 

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  • Deputy Sheriffs

I have made a note to investigate this further. However it's not the highest priority right now but we'll check eventually.

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2 hours ago, Secondator said:

I have made a note to investigate this further. However it's not the highest priority right now but we'll check eventually.

 

No problem. I figured it's more of an icing-on-the-cake kind of thing.

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